Electronically tunable microwave filter

ABSTRACT

An electronically tunable &#39;&#39;&#39;&#39;YIG&#39;&#39;&#39;&#39; sphere filter having plural sphere coupling in combination with input and output loop couplings for the first and last spheres, the structure providing performance characteristics not obtainable with ordinary loop coupling using a single or multiple gyromagnetic spheres. These characteristics include low inserion loss, wide tunable bandwidth, and wide constant instantaneous bandwidth, making the filter particularly suitable for superheterodyne electronic countermeasure receivers using multiple octave ranges.

United States Patent [19] Cohen June 28, 1974 ELECTRONICALLY TUNABLE MICROWAVE FILTER [75] Inventor: Morris Cohen, Oceanside, NY. [73] Assignee: Loral Corporation, New York, NY.

[22] Filed: Mar. 12, 1973 [2]] Appl. N0.: 340,573

[52] US. Cl. 333/73 C, 333/73 W [51] Int. Cl. H01!) 1/20 [58] Field Of Search... 333/73 R, 73 C, 73 S, 73 W, 333/24.l, 24.2

[56] References Cited UNITED STATES PATENTS 3,290,625 12/1966 Bartram et al. 333/73 R 3,368,169 2/1968 Carter et al. 333/73 S 3,435,385 3/1969 Cohen 333/73 C 3,611,197 10/1971 Moore et al. 333/73 S X Primary Examiner-Paul L. Gensler Attorney, Agent, or Firm-Charles E. Temko ABSTRACT An electronically tunable YIG" sphere filter having plural sphere coupling in combination with input and output loop couplings for the first and last spheres, the structure providing performance: characteristics not obtainable with ordinary loop coupling using a single or multiple gyromagnetic spheres. These characteristics include low inserion loss, wide tunable bandwidth, and wide constant instantaneous bandwidth, making the filter particularly suitable for superheterodyne electronic countermeasure receivers using multiple octave ranges.

1 Claim, 1 Drawing Figure l ELECTRONICALLY TUNABLE MICROWAVE FILTER This invention relates generally to electronically tunable microwave filters, and more particularly to one employing the characteristics of ytrium-iron-garnet (YIG) spheres. Devices of this general type are known in the art, and the invention lies in specific constructional details permitting improved performance.

BRIEF DESCRIPTION OF THE PRIOR ART BRIEF DESCRIPTION OF THE PRESENT INVENTION Briefly stated, the invention contemplates the provision of a YIG sphere electronically tunable microwave filter including a plurality of spheres mutually positioned to permit sphere-to-sphere coupling via the external magnetic field set up in each sphere. This is accomplished by providing a cylindrical or square tube,

and positioning the spheres in the tube. The input and output rf power is coupled via a loop to the first and last spheres. When the composite structure is immersed in a magnetic field H and the spheres are resonated, the rf frequency f is coupled from the input loop to the output loop of the filter by the external magnetic field of one sphere to that of the other sphere, and so on through the array of spheres. The degree of coupling is dependent upon the size of the spheres and the spacing between them. The skirt selectively of the filter is dependent upon the number of spheres in the array.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT In accordance with the invention, the device, generally indicated by reference character comprises a cylindrical tube 11 of approximately 0.06 inches internal diameter and formed of non-magnetic metallic material. The tube extends for a length of approximately one inch between first and second ends 13 and 14, respectively. Supported on adjustable dielectric rods for tuning l5 and 16 are an input YIG sphere l7 and an output YIG sphere l8 whichare grounded as known in the art.

Communicating with the spheres l7 and 18 are first and second coaxial transmission lines 19 and 20, the first line 19 having a terminal 22 supporting an input loop 23, the second line, having a terminal 24 supporting an output loop 25 coupling with the spheres 17 and 18, respectively, in well known manner.

Communicating with the tube 11 are first and second metal sleeves 26 and 27 supporting dielectric rods 28 and29 respectively, the ends of the rods adjustably positioning the third and fourth YIGspheres 30 and 31 which are also grounded in coaxial position with re- I spect to the ends of the tube 11, the interstitial distance 2 between the spheres 17, 18, 30 and 31 being substantially equal.

The required external magnetic field is provided between a north pole 32 and south pole 33 of an external magnet, again as known in the art.

THEORY OF OPERATION In essence, the filter utilizes garnet spheres as resonators, and is tuned over a frequency range by means of the electromagnet. The resonant frequency (f.,) of the YIG spheres is determined by the field dc) Produced by the electromagnet.

The single-crystal YIG sphere contains unpaired electrons which yield magnetic moments as a result of their spins. When a dc field is applied to the sphere, the

spin magnetic moments will precess about the axis of the applied H field at a rate: f, (MHz) 2.8 H (oersteds) The sense of precession is dependent upon the direction of the H field.

In the present device, instead of providing input and output loops surrounding a single or multiple spheres, the input energy is coupled through the spheres via the external magnetic field set up in each sphere.

MEASURED PERFORMANCE DATA A typical set of data taken of a K -band filter is given below.

An added advantage of the disclosed filter lies in the fact that the cylindrical (or square) tube structure behaves as a waveguide beyond cutoff and therefore affords greater solation between input and output loops than the standard loop-coupled filter.

The relatively constant 3 dB bandwidth, and low insertion loss over the tested range may be observed from the above data.

I wish it to be understood that I do not consider the invention limited to the precise details of structure which the invention pertains.

I claim:

1. In an electronically tunable gyromagnetic sphere filter for coupling apair of transmission lines, and ineluding means for" producing an external magnetic field, the improvement comprising: a hollow substantially uniform diameter tube, of non-magnetic metallic material, a plurality of gyromagnetic spheres in mutually spaced relation disposes within said tube along the principal axis thereof, input loop means surrounding one of said plurality of spheres, and connected to one of said transmission lines, and output loop means surrounding another of said plurality of spheres, and connected to the other of said transmission lines, whereby when said spheres are placed within an external magnetic field produced by said first mentioned means, said spheres will couple to each other via said external magnetic field. 

1. In an electronically tunable gyromagnetic sphere filter for coupling a pair of transmission lines, and including means for producing an external magnetic field, the improvement comprising: a hollow substantially uniform diameter tube, of non-magnetic metallic material, a plurality of gyromagnetic spheres in mutually spaced relation disposes within said tube along the principal axis thereof, input loop means surrounding one of said plurality of spheres, and connected to one of said transmission lines, and output loop means surrounding another of said plurality of spheres, and connected to the other of said transmission lines, whereby when said spheres are placed within an external magnetic field produced by said first mentioned means, said spheres will couple to each other via said external magnetic field. 